The present invention relates generally to the field of monitors and measurement devices for electrical power. More particularly, the invention relates to techniques for determining impedance parameters of electrical power, particularly power distributed via a power distribution grid.
A wide range of applications exists for power monitors and devices capable of determining parameters of electrical power. For example, in many application unwanted conditions can arise in loads, distribution equipment and lines, the severity of which is a function of the line impedance. For example, the line impedance is a precursor to calculating short circuit current, arc current, available energy, and other important features of electrical power. Because these currents and energies can flow or be released during a fault condition or other unwanted, or even desired situations, knowing the power line impedance is of considerable importance.
Various methods exist in the art for calculating or attempting to determine power line impedance. For example, impedance can be computed based upon nameplate information on certain equipment, in addition to knowledge of the physical and electrical characteristics of distribution components. Transformers, for example, typically carry nameplate information regarding impedance as a percentage value. Knowledge of the size and length of electrical conductors, and the characteristics of other intermediate components between the transformer and a load can be used to calculate or estimate the impedance at particular points in a system. However, such techniques are highly imprecise, and rely upon some degree of estimation as to the actual characteristics of the components and transmission lines.
Techniques have also been developed for directly measuring impedance of power lines. Such techniques have permitted some degree of knowledge of the power line impedance, but are still somewhat imprecise or incomplete. For example, known techniques do not typically permit measurement of both inductive and resistive components of the power line impedance. While one of these components may generally dominate the impedance measurement, both components are important for determining the actual characteristics of the current and energy that can be released by the power line, particularly during transient periods such as faults.
There is a need in the art for improved techniques for measuring and determining impedance of power sources. There is a particular need for a technique that would permit accurate measurement of power line impedance, including both resistive and inductive components thereof.